In wood construction, architectural members such as columns, studs, girders, and beams, all made of wood, are used. In assembling a column with a girder, for instance, the so-called mortise-and-tenon joint in which a tenon of one member is snugly fitted into a mortise formed in the other member is generally employed. There also are cases in which metal fasteners are used to reinforce the joint between wooden architectural members.
However, in the above construction system, the mortises and tenons must be intricate in structure and require high dimensional precision so that the construction time is prolonged.
Therefore, recent years have witnessed an increasing popularity of prefabricated homes even in the field of wood construction where factory-manufactured wooden architectural members are assembled at sites of construction. For reducing the construction time and cost in this field, convenient, high-strength joint and metal fasteners are being used in lieu of mortise-and-tenon joints which require delicate workmanship and metal fasteners of various configurations have so far been proposed.
However, since wooden architectural members are hygroscopic, the problem of rot due to dew condensation tends to take place. Moreover, as the result of the widespread use of insulation materials for insuring effective air conditioning and the hermetic sealing of the rooms in recent years, dew condensation is more liable to occur than before between the exterior and interior walls or sidings. Such dew formation not only causes rusting of metal joints and reinforcing metal members but the moisture trapped between the metal member and the adjoining wood encourages growth of various wood-decaying microorganisms so that the wood easily begins to rot in the vicinity of the joints.
To overcome the above disadvantages, metal members subjected to rust-proofing treatment such as molten zinc plating have been utilized in recent years but such fasteners are not fully effective in preventing wood rot.